The present invention relates generally to an apparatus for decoding of composite video to provide high quality serial digital output and, more particularly, to a combination of unique circuits including a three-dimensional comb filter for providing better separation of composite video into luminance and chrominance components, and an optional interpolation circuit for removing any time-base errors on the composite video input.
During the transition to digital television (DTV) production and broadcasting, high quality decoding of composite video signals to produce a serial digital signal is essential to produce digital signals that are comparable to those that originate as digital signals. For signals that originate as composite video, the quality of the DTV signal at the end of the transmission system is only as good as the initial conversion to serial digital interface (SDI). Improper decoding can leave artifacts which, although normally masked in the current National Television System Committee (NTSC) and Phase Alternating Line (PAL) standards, show up as visible errors when viewed on digital television sets. Decoded composite signals may have vertical smear, color errors at vertical transitions, grainy noise, loss of horizontal resolution in both the luminance (luma) and chrominance (chroma) signals, and contouring effects. Also, once a composite signal is decoded incorrectly it may be impossible to fix the problems that are created.